1. Field of the Invention
The present invention relates generally to prosthetic feet. More particularly, the present invention relates to prosthetic feet with an energy transfer medium including a variable viscosity fluid.
2. Related Art
Many individuals have lost a limb for various reasons including war, accident, or disease. In most instances, these individuals are not only able to live relatively normal lives, but physically active lives as well. Often times, these individuals are aided in their everyday lives by a prosthetic limb. The objective of prosthesis is to provide an artificial limb that simulates the function and natural feel of the replaced limb.
With respect to prosthetic feet, the development of a functional and natural artificial foot has been limited only by material and imagination. Many designs have attempted to copy the anatomy of the foot or simulate its actions by replacing the bones and muscle with various mechanical components. Other designs have departed radically from mere anatomical copying or mechanical simulation by replacing the entire foot with an energy storage element, such as a spring. As the user steps onto the foot, the user's weight compresses the spring. As the user moves forward, the user's weight comes off the foot and the energy stored in the spring is used to propel the user forward. Examples of such energy storing, spring-like feet include U.S. Pat. Nos. 5,037,444; 4,547,913; 5,181,932 and 5,976,191.
The prosthetic feet typically include spring-like members that are typically flexible and resilient. In order to provide a natural feel and cushion of a natural foot, the members must be flexible and deflect under the user's weight. Such flexibility and the ability to deflect often require the members forming the foot to be structurally weak, or more flexible. On the other hand, it is desirable to make the members as strong or stiff as possible from a structural and durability standpoint. Thus, there may be a trade-off between obtaining a sufficient cushion or feel, with members that are weak or flexible and over-deflect, and obtaining a solid and durable structural foot, with stiffer members.
The stiffness of prosthetic feet typically varies according to the intended use. Feet intended for everyday use typically require a soft feel, and thus incorporate a softer spring. Feet intended for athletic use typically require strength, and thus incorporate a stiff spring. Feet designed for particular purposes are typically unsuited for other purposes. Stiff, athletic feet are too hard for everyday use, and soft, everyday feet are too fragile for athletic use. Multiple-use feet have been designed which are capable of many different uses, but without being particularly well suited for any specialized use.
In addition, users may have different weights. Thus, prosthetic feet may require a high degree of custom design, or be particularly tailored to the individual user. However, it is desirable from a cost and manufacturing standpoint to create a foot that is usable by many sizes of individuals.